1. Field of the Invention
The invention concerns a device and a method to measure the beam spot of a particle beam and a system to generate a particle beam by means of such a device. The invention is used widely in particle therapy, where the cross section of a particle beam is to be measured.
2. Description of the Prior Art
Particle therapy is an established process to treat tissue, specifically tissue containing tumors. However, irradiation processes used in particle therapy are also used in non-therapeutic applications. This includes, for example, research with particle therapy applied to non-living units or bodies, irradiation of materials, and others. Charged particles, such as protons, carbon ions, or other types of ions are accelerated to high energy levels, bundled into a particle beam and sent to one or more treatment rooms via a high energy beam transport system. The object to be irradiated is irradiated with the particle beam in one of these treatment rooms.
The particle beam is characterized by various parameters. They include, for example, the position and energy level of the particle beam. In addition to these parameters, the beam width—also known as beam focus—is important.
For irradiation, it is often assumed as an ideal that the distribution of particles within the two-dimensional cross section, which is also known as the beam spot, is distributed as a normal distribution. A significant variance from such a normal distribution of the beam spot may have a significant impact on the distribution of the applied dose. Likewise in the case of beam spots that are not normally distributed, which may have different distributions in varying directions, the assumptions regarding the beam spot are critical for the distribution of the applied dose. Thus, it is important to survey the beam spot of a particle beam with precision. This may be done, for example, by regular quality assurance measures.
In order to survey the beam spot, and thus to determine the beam width, radiographic film is usually used today. The film is irradiated with the particle beam, and the pattern registered on the film is then evaluated. However, this process is relatively slow and costly.
In addition, the option of measuring the beam width in so-called multi-wire proportional chambers (MWPC) is known. Such a chamber usually contains a number of wires that are parallel to each other. Wires parallel in one direction facilitate the measurement of the projection of the beam spot in a perpendicular direction. An MWPC often contains two sets of parallel wires that are perpendicular to each other. This permits a measurement of the projection of the beam spot in these two directions.
Furthermore, the option is known to use display screens to measure the beam spot. The beam spot may be measured here directly in two dimensions. However, a disadvantage for quantitative evaluation results from interference from ambient light. Thus, at least the system of the camera and the screen or even the entire room must be darkened.